Despite recent improvement in efficiency, CdS/CdTe heterojunction solar cells perform significantly below the theoretical limit based on the band gap of CdTe. Several design enhancements to improve the efficiency of these solar cells have been proposed, including alternative solar cell designs and the incorporation of additional elements into the existing design of CdS/CdTe solar cells. For example, a tandem junction cell design which incorporates a CdTe-based ternary alloy with a higher band gap as a p-type absorber in the top cell may exhibit higher efficiency. As another example, the efficiency of the existing CdS/CdTe heterojunction solar cell may be enhanced by the inclusion of an electron reflector (ER) structure in the form of a CdTe-based ternary alloy layer. In both cases, the CdTe-based ternary alloy may be a high band gap alloy, such as Cd1-xMgxTe.
The widespread adoption of these design enhancements of CdS/CdTe heterojunction solar cells may be hampered in part by the lack of methods to produce Cd1-xMgxTe layers of sufficient quality on a large scale. Existing methods of Cd1-xMgxTe deposition, including RF sputtering and co-evaporation methods such as side-by-side close-source sublimation (CSS) methods, are known to produce good quality Cd1-xMgxTe films, but these existing methods are typically slow and demonstrate poor spatial uniformity, rendering these methods unsuitable for use in large scale manufacturing.
A need exists for improved systems and methods for the deposition of high quality Cd1-xMgxTe films rapidly, over large areas, and with high spatial uniformity. These improved systems and methods would eliminate a significant barrier to realizing and commercializing the potential efficiency improvements to solar cells described above.